diff --git a/docs/decisions/README.md b/docs/decisions/README.md
index bd8d1147a..be3763c5f 100644
--- a/docs/decisions/README.md
+++ b/docs/decisions/README.md
@@ -161,6 +161,7 @@ the link for rationale. Superseded/retired history lives in `archive/`. Regenera
 | `spa.deco-templates-table` | The deco-templates editor also renders its day/deco assignment as a table, extending (not replacing) the templates-editor-table convention. | 2026-07-09 | [link](records/spa/deco-templates-table.md) |
 | `spa.download-sample-gate` | The SPA disables both Download Media Sample and Download Results while a troubleshooting session is starting/running (Blazor only gated Download Results). | 2026-07-09 | [link](records/spa/download-sample-gate.md) |
 | `spa.legacy-redirect-matcher` | `LegacyUiRedirects.TryGetRedirect` is a two-tier matcher — an exact `OrdinalIgnoreCase` `Map` (Tier 1) then an ordered segment-template pattern list (Tier 2, first-match-wins) — collision-free by construction, with a guard invariant that no rule may prefix-match `/api`, `/artwork`, `/docs`, `/openapi`, `/iptv`, `/app`, or `/media/sources`. | 2026-07-11 | [link](records/spa/legacy-redirect-matcher.md) |
+| `spa.list-completeness-vs-bounded-pickers` | The shared `loadAllPages` helper (`web/src/api/paging.ts`) pages a `/api/v1` list to completeness against `totalCount` and is used ONLY for lists that are bounded by construction (rerun collections, multi-collections, playlists — admin-created, hundreds of rows at most). A `getLibraryBrowseItems` picker over a media-library table (Episode/Song/Image/Movie/MusicVideo, tens of thousands of rows possible) must NOT page to completeness — it fetches ONE bounded page (the server cap) and surfaces the truncation (a `ctv-field-help` hint wired to the real `totalCount`) instead of silently dropping the rest. | 2026-07-26 | [link](records/spa/list-completeness-vs-bounded-pickers.md) |
 | `spa.logs-page-size-local` | The Logs page rows-per-page preference is stored in `window.localStorage` (`ctv-logs-page-size`), not a server `ConfigElement`. | 2026-07-11 | [link](records/spa/logs-page-size-local.md) |
 | `spa.playback-troubleshoot-poll` | The playback-troubleshooting screen reports FFmpeg completion by polling `GET /api/troubleshoot/playback/status` (~2s) rather than a server push channel. | 2026-07-09 | [link](records/spa/playback-troubleshoot-poll.md) |
 | `spa.playout-reset-button` | The SPA keeps a single Reset action (server picks the default build mode) and drops Blazor's separate "Schedule reset" button since its capability already exists via the playout's Edit-details flow. | 2026-07-09 | [link](records/spa/playout-reset-button.md) |
diff --git a/docs/decisions/records/spa/list-completeness-vs-bounded-pickers.md b/docs/decisions/records/spa/list-completeness-vs-bounded-pickers.md
new file mode 100644
index 000000000..d3fb07ebc
--- /dev/null
+++ b/docs/decisions/records/spa/list-completeness-vs-bounded-pickers.md
@@ -0,0 +1,53 @@
+---
+key: spa.list-completeness-vs-bounded-pickers
+title: '2026-07-26 — `loadAllPages` is for bounded-by-construction lists only; media-library pickers stay bounded and show truncation (#644 follow-up)'
+status: active
+since: '2026-07-26'
+supersedes: none
+superseded-by: none
+rule: 'The shared `loadAllPages` helper (`web/src/api/paging.ts`) pages a `/api/v1` list to completeness against `totalCount` and is used ONLY for lists that are bounded by construction (rerun collections, multi-collections, playlists — admin-created, hundreds of rows at most). A `getLibraryBrowseItems` picker over a media-library table (Episode/Song/Image/Movie/MusicVideo, tens of thousands of rows possible) must NOT page to completeness — it fetches ONE bounded page (the server cap) and surfaces the truncation (a `ctv-field-help` hint wired to the real `totalCount`) instead of silently dropping the rest.'
+signals: '`loadAllPages`, Class A vs Class B picker, LuceneSearchIndex.Search hitsLimit, picker truncation hint, ctv-field-help, PagedResult, `complete` flag · paths: `web/src/api/paging.ts`, `web/src/screens/RerunCollectionsScreen.tsx`, `web/src/screens/PlaylistsScreen.tsx`, `web/src/screens/FillerPresetsScreen.tsx`, `web/src/screens/MultiCollectionsScreen.tsx`, `docs/spa-conventions.md` §3b · issues: #644'
+mechanics: '`docs/spa-conventions.md` §3b'
+---
+
+`fe342a6a` (#644) extracted the `loadAllPages` client-side paging helper and applied it at every
+call site that had been requesting an over-cap `pageSize` to "get everything in one call" — a
+pattern that silently truncated to the server's `MaxPageSize` (100) with no error and no
+truncation indicator. A cold adversarial review of that fix found it was correct for the
+admin-created lists (rerun collections, multi-collections, playlists — bounded by construction,
+hundreds of rows at most) but dangerous for three call sites: the `getLibraryBrowseItems` pickers
+in `RerunCollectionsScreen`, `PlaylistsScreen`, and `FillerPresetsScreen`, which populate a native
+`<select>` whose `mediaType` can be `Episode`, `Song`, `Image`, `Movie`, or `MusicVideo` — the
+largest tables in an install. Paging one of those to completeness means on the order of 200 serial
+requests against a 20,000-row library, each **more** expensive than the last (`LuceneSearchIndex
+.Search` computes `hitsLimit = skip + limit`, so later pages re-scan a growing prefix), ending in a
+`<select>` with 20,000 `<option>` nodes rendered into the DOM. That is worse than the defect #644
+set out to fix.
+
+The fix keeps `loadAllPages` unchanged in behavior for the bounded lists (it now also reports a
+`complete: boolean` flag and accepts an `AbortSignal`, per the same follow-up review's F4/F2
+findings) and removes it entirely from the three media-library picker call sites. Those instead
+call `getLibraryBrowseItems` directly for a single page at the server cap (`pageSize: 100`) and
+read the response's `totalCount` to detect truncation. The defect named in #644's title is
+"*silently* truncate" — the silence is the bug, not the bound. So a truncated picker load renders a
+`ctv-field-help` hint next to the `<select>` (`Showing the first 100 of 5000 — use search to
+narrow.`) instead of either paging forever or truncating without saying so. A full
+typeahead/search-driven picker over the media library is a materially larger feature (a `query`
+param already exists on `getLibraryBrowseItems` for it) and is deliberately out of scope here — a
+follow-up issue, not this fix.
+
+**2026-07-26 addendum (round-3 review F1):** `loadPickerOptions`'s `multi` branch (a Class A
+source — `MultiCollection`) reused the same `truncated: boolean` field as the Class B media-library
+pickers, but the two conditions are not the same thing: Class B's `truncated` means "there are more
+rows than fit in one page — narrow via search," while a Class A picker's flag meant "the
+`loadAllPages` loop didn't converge" (`complete: false`) — a defensive/incomplete load, not a cap.
+Rendering both through the shared "Showing the first N of M — use search to narrow" copy produced a
+self-contradictory "Showing the first 47 of 47" on an incomplete Class A load, pointing at a search
+box that picker doesn't have. `RerunCollectionsScreen.tsx`/`PlaylistsScreen.tsx` now return a
+`hint: 'incomplete' | 'none' | 'truncated'` discriminator instead of a boolean, and render distinct
+copy per value — `'truncated'` keeps the existing search-narrowing text, `'incomplete'` renders
+"List may be incomplete — retry to reload" (matching the wording already used for the Class A
+list-load warn `Badge`). A picker's `console.warn` on an incomplete load — and the analogous one in
+`SchedulesScreen.loadAllRerunCollections` — is also gated on `!signal?.aborted`, so a superseded or
+user-aborted load (Retry, or a type switch mid-load) no longer logs a false "did not complete"
+warning.
diff --git a/docs/spa-conventions.md b/docs/spa-conventions.md
index 4d55f7906..c7c4c016b 100644
--- a/docs/spa-conventions.md
+++ b/docs/spa-conventions.md
@@ -121,6 +121,70 @@ Convention — when a screen keeps stale results visible during a refetch:
   current (compare against a ref that always holds the committed value — `SearchScreen` reuses
   `lastQueryRef`) and **discard** otherwise. Checking only `activeRef` (mounted) is insufficient.
 
+## 3b. Paged list endpoints clamp server-side — page to completeness ONLY for bounded lists, never a media-library picker
+
+Every paged `/api/v1` list endpoint (rerun-collections, multi-collections, library/browse, search,
+trakt-lists, …) clamps `pageSize` to its own controller's `MaxPageSize` (100, as of #644) regardless
+of what the client requests. A screen that asks for `pageSize: 1000` to "get everything in one call"
+gets only the first `MaxPageSize` rows back, silently — no error, no truncation indicator, no paging
+UI to notice the gap. This was issue #644 (following on from #634, which fixed the first instance —
+`SchedulesScreen`'s rerun-collections picker load).
+
+**Two classes of call site, treated differently** (decision record:
+`docs/decisions/records/spa/list-completeness-vs-bounded-pickers.md`, `spa.list-completeness-vs-bounded-pickers`
+— a #644 follow-up review found the original blanket "use `loadAllPages` for any picker" guidance
+below was itself the defect for one class of caller):
+
+- **Bounded-by-construction lists** (rerun collections, multi-collections, playlists — admin-created,
+  hundreds of rows at most): genuinely need the complete list, and completeness is cheap. Use the
+  shared `loadAllPages` helper (`web/src/api/paging.ts`, re-exported via `web/src/api/index.ts`)
+  instead of an inflated `pageSize`:
+
+  ```ts
+  const { items, complete } = await loadAllPages(getMultiCollections); // pages against totalCount, cap defaults to 100
+  ```
+
+  It pages `pageNum` from 0 (per §"paging-zero-based" in `api-conventions.md`) against the response's
+  `totalCount`, stopping — and reporting `complete: false` — on an empty page (defensive guard
+  against a `totalCount` that never converges) or on an aborted `signal`. **Always check `complete`**:
+  a caller that needs the full list must not treat a resolved promise as proof the list is whole (a
+  partial result is otherwise silently indistinguishable from a complete one — the same defect class
+  as #644 itself, since `GetLibraryBrowseItemsHandler.HydrateMediaItems` can legitimately drop stale
+  Lucene hits and produce a short/empty page in normal operation). Pass an `AbortSignal` (4th arg)
+  from the caller's effect cleanup so a superseded load stops issuing further page requests instead
+  of hammering the server for a result nobody will see. **Do not raise the server-side cap to work
+  around this** — the `api.search-allitems-paging` precedent is that the client pages and the server
+  stays bounded; that's a backend decision, out of scope for a screen fix.
+
+- **Media-library pickers** (`getLibraryBrowseItems` backing a `<select>` for Episode / Song / Image /
+  Movie / MusicVideo / etc. — the largest tables in an install, tens of thousands of rows possible):
+  must **NOT** use `loadAllPages`. Paging to completeness here means on the order of 200 serial
+  requests for a 20k-row library — each more expensive than the last, since
+  `LuceneSearchIndex.Search` computes `hitsLimit = skip + limit` — to populate a native `<select>`
+  with thousands of `<option>` nodes. That is worse than the truncation bug it would "fix". Instead,
+  fetch **one bounded page** directly (`pageSize` at the cap) and make the truncation **visible**
+  rather than silent — e.g. a `ctv-field-help` hint next to the picker: `Showing the first 100 of
+  5000 — use search to narrow.` (wire the response's real `totalCount`). See
+  `RerunCollectionsScreen.tsx`/`PlaylistsScreen.tsx`/`FillerPresetsScreen.tsx`'s `loadPickerOptions`
+  for the pattern. A full typeahead/search-driven picker is a separate, larger feature — out of scope
+  for this fix.
+
+  **A Class B truncation and a Class A `complete: false` are different conditions — don't collapse
+  them into one boolean** (#644 follow-up round-3 review F1): a `loadPickerOptions` result that can
+  come from either a Class A (`loadAllPages`) or Class B (single bounded page) source should carry a
+  `hint: 'incomplete' | 'none' | 'truncated'` discriminator, not a `truncated: boolean` reused for
+  both. `'truncated'` (Class B, an expected cap) keeps the "Showing the first N of M — use search to
+  narrow" copy; `'incomplete'` (Class A, `loadAllPages`'s `complete: false`) renders different copy
+  ("List may be incomplete — retry to reload") — rendering both through the search-narrowing text
+  produces a self-contradictory "Showing the first 47 of 47" when a Class A load doesn't converge.
+  Also gate any `console.warn` on a Class A `complete: false` with `!signal?.aborted` — a superseded
+  or user-aborted load returns `complete: false` too, and that's expected, not a defect.
+
+**If a screen shows a bounded preview or has real paging UI** (a "load more" button, a page-size
+selector, a fixed-size typeahead result list), a `pageSize` at or below the cap is correct as-is —
+`loadAllPages` is only for "I need literally everything, and the list is small by construction"
+call sites.
+
 ## 4. API client modules
 
 One file per domain in `web/src/api/`, e.g. `logs.ts`, `blocks.ts`, `playouts.ts`. Pattern (see
diff --git a/web/src/api/index.ts b/web/src/api/index.ts
index 0fc10728f..181107266 100644
--- a/web/src/api/index.ts
+++ b/web/src/api/index.ts
@@ -23,6 +23,7 @@ export * from './mediaDetail';
 export * from './mediaItems';
 export * from './mediaSources';
 export * from './multiCollections';
+export * from './paging';
 export * from './pickers';
 export * from './playlists';
 export * from './playoutHistory';
diff --git a/web/src/api/paging.test.ts b/web/src/api/paging.test.ts
new file mode 100644
index 000000000..6815c79e1
--- /dev/null
+++ b/web/src/api/paging.test.ts
@@ -0,0 +1,287 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { loadAllPages, type PagedResult, type PagingParams } from './paging';
+import { getMultiCollections } from './multiCollections';
+import { getLibraryBrowseItems } from './libraryBrowse';
+
+function jsonResponse(body: unknown, status = 200): Response {
+  return new Response(JSON.stringify(body), {
+    headers: { 'Content-Type': 'application/json' },
+    status
+  });
+}
+
+// Builds a "server" of `total` items with predictable ids/names, clamped to `cap` per page —
+// mirrors the real RerunCollectionController/MultiCollectionController/LibraryBrowseController
+// behavior (MaxPageSize=100 for all three, confirmed by reading the controllers for #644).
+function fakeItem(id: number) {
+  return { id, name: `item-${id}` };
+}
+
+describe('loadAllPages', () => {
+  it('stops after a single page when totalCount fits within pageSize', async () => {
+    const fetchPage = vi.fn(async (params: { pageNum?: number; pageSize?: number }): Promise<PagedResult<{ id: number }>> => {
+      expect(params.pageNum).toBe(0);
+      expect(params.pageSize).toBe(100);
+      return { page: [fakeItem(1), fakeItem(2)], totalCount: 2 };
+    });
+
+    const result = await loadAllPages(fetchPage);
+
+    expect(result).toEqual({ complete: true, items: [fakeItem(1), fakeItem(2)] });
+    expect(fetchPage).toHaveBeenCalledTimes(1);
+  });
+
+  it('pages to completeness across more than one page boundary (250 items @ cap 100 -> 3 requests)', async () => {
+    const total = 250;
+    const cap = 100;
+    const all = Array.from({ length: total }, (_, i) => fakeItem(i + 1));
+
+    const fetchPage = vi.fn(async (params: { pageNum?: number; pageSize?: number }): Promise<PagedResult<{ id: number }>> => {
+      const pageNum = params.pageNum ?? 0;
+      const pageSize = params.pageSize ?? cap;
+      const start = pageNum * pageSize;
+      return { page: all.slice(start, start + pageSize), totalCount: total };
+    });
+
+    const result = await loadAllPages(fetchPage, undefined, cap);
+
+    expect(fetchPage).toHaveBeenCalledTimes(3);
+    expect(fetchPage.mock.calls.map((call) => call[0])).toEqual([
+      { pageNum: 0, pageSize: 100 },
+      { pageNum: 1, pageSize: 100 },
+      { pageNum: 2, pageSize: 100 }
+    ]);
+
+    expect(result.complete).toBe(true);
+
+    // Pin the exact set: ids 1..250 in order, nothing dropped at either page boundary.
+    expect(result.items.map((item) => item.id)).toEqual(Array.from({ length: total }, (_, i) => i + 1));
+    expect(result.items[99]).toEqual(fakeItem(100));
+    expect(result.items[100]).toEqual(fakeItem(101));
+    expect(result.items[249]).toEqual(fakeItem(250));
+  });
+
+  it('threads extra base params (e.g. mediaType) into every page request', async () => {
+    const fetchPage = vi.fn(async (): Promise<PagedResult<{ id: number }>> => ({ page: [fakeItem(1)], totalCount: 1 }));
+
+    await loadAllPages(fetchPage, { mediaType: 'Movie' });
+
+    expect(fetchPage).toHaveBeenCalledWith({ mediaType: 'Movie', pageNum: 0, pageSize: 100 });
+  });
+
+  it('breaks on an empty page even if totalCount claims more remain (defensive, never loops forever) and reports incomplete', async () => {
+    const fetchPage = vi.fn(async (params: { pageNum?: number }): Promise<PagedResult<{ id: number }>> => {
+      if ((params.pageNum ?? 0) === 0) {
+        return { page: [fakeItem(1)], totalCount: 5 };
+      }
+      return { page: [], totalCount: 5 };
+    });
+
+    const result = await loadAllPages(fetchPage);
+
+    expect(result).toEqual({ complete: false, items: [fakeItem(1)] });
+    expect(fetchPage).toHaveBeenCalledTimes(2);
+  });
+
+  it('a short-but-non-empty page keeps requesting, then reports incomplete once a later page comes back empty', async () => {
+    // First page under-fills (1 item though pageSize is 100) but totalCount claims 5 remain, so the
+    // loop must keep going by actual accumulated length, not by whether the page "looked full".
+    const calls: Array<number | undefined> = [];
+    const fetchPage = vi.fn(async (params: { pageNum?: number }): Promise<PagedResult<{ id: number }>> => {
+      calls.push(params.pageNum);
+      if ((params.pageNum ?? 0) === 0) {
+        return { page: [fakeItem(1)], totalCount: 5 };
+      }
+      if ((params.pageNum ?? 0) === 1) {
+        return { page: [fakeItem(2), fakeItem(3)], totalCount: 5 };
+      }
+      return { page: [], totalCount: 5 };
+    });
+
+    const result = await loadAllPages(fetchPage);
+
+    expect(result).toEqual({ complete: false, items: [fakeItem(1), fakeItem(2), fakeItem(3)] });
+    expect(fetchPage).toHaveBeenCalledTimes(3);
+  });
+
+  it('treats a null/undefined totalCount as "just this page" and reports complete', async () => {
+    const fetchPage = vi.fn(async (): Promise<PagedResult<{ id: number }>> => ({ page: [fakeItem(1), fakeItem(2)], totalCount: undefined }));
+
+    const result = await loadAllPages(fetchPage);
+
+    expect(result).toEqual({ complete: true, items: [fakeItem(1), fakeItem(2)] });
+    expect(fetchPage).toHaveBeenCalledTimes(1);
+  });
+
+  it('treats a null page as empty and reports complete with zero items', async () => {
+    const fetchPage = vi.fn(async (): Promise<PagedResult<{ id: number }>> => ({ page: null, totalCount: null }));
+
+    const result = await loadAllPages(fetchPage);
+
+    expect(result).toEqual({ complete: true, items: [] });
+    expect(fetchPage).toHaveBeenCalledTimes(1);
+  });
+
+  it('propagates a rejection on page 2 without retrying or issuing further requests', async () => {
+    const fetchPage = vi.fn(async (params: { pageNum?: number }): Promise<PagedResult<{ id: number }>> => {
+      if ((params.pageNum ?? 0) === 0) {
+        return { page: [fakeItem(1)], totalCount: 3 };
+      }
+      throw new Error('page 2 failed');
+    });
+
+    await expect(loadAllPages(fetchPage)).rejects.toThrow('page 2 failed');
+    expect(fetchPage).toHaveBeenCalledTimes(2);
+  });
+
+  it('cancellation: an already-aborted signal issues no requests at all', async () => {
+    const fetchPage = vi.fn(async (): Promise<PagedResult<{ id: number }>> => ({ page: [fakeItem(1)], totalCount: 1 }));
+    const controller = new AbortController();
+    controller.abort();
+
+    const result = await loadAllPages(fetchPage, undefined, 100, controller.signal);
+
+    expect(result).toEqual({ complete: false, items: [] });
+    expect(fetchPage).not.toHaveBeenCalled();
+  });
+
+  it('cancellation: aborting after page 1 stops the loop from issuing page 2 or later', async () => {
+    const total = 250;
+    const cap = 100;
+    const all = Array.from({ length: total }, (_, i) => fakeItem(i + 1));
+    const controller = new AbortController();
+
+    const fetchPage = vi.fn(async (params: { pageNum?: number; pageSize?: number }): Promise<PagedResult<{ id: number }>> => {
+      const pageNum = params.pageNum ?? 0;
+      const pageSize = params.pageSize ?? cap;
+      if (pageNum === 0) {
+        // Abort as soon as the first page resolves, before the loop issues its next request.
+        controller.abort();
+      }
+      const start = pageNum * pageSize;
+      return { page: all.slice(start, start + pageSize), totalCount: total };
+    });
+
+    const result = await loadAllPages(fetchPage, undefined, cap, controller.signal);
+
+    // The whole point: assert the CALL COUNT stayed at 1 — no page 2/3 request was ever issued.
+    expect(fetchPage).toHaveBeenCalledTimes(1);
+    expect(result).toEqual({ complete: false, items: all.slice(0, cap) });
+  });
+
+  it('type-level: baseParams is required when the loader params type has a required field beyond pageNum/pageSize (F6)', () => {
+    interface RequiredExtraParams extends PagingParams {
+      requiredThing: string;
+    }
+    const fetchPage: (params: RequiredExtraParams) => Promise<PagedResult<{ id: number }>> = async () => ({
+      page: [],
+      totalCount: 0
+    });
+
+    // @ts-expect-error baseParams is required here — omitting it must NOT compile (the old
+    // `= {} as Omit<P, ...>` default silently defeated this check for every P, #644 follow-up F6).
+    void loadAllPages(fetchPage);
+
+    // The correctly-called form still type-checks.
+    void loadAllPages(fetchPage, { requiredThing: 'ok' });
+  });
+});
+
+describe('loadAllPages against real domain loaders', () => {
+  beforeEach(() => {
+    window.localStorage.clear();
+    vi.restoreAllMocks();
+  });
+
+  it('getMultiCollections: pins the exact merged set across a >cap (250-item) list and asserts fetch call params', async () => {
+    const total = 250;
+    const cap = 100;
+    const all = Array.from({ length: total }, (_, i) => ({ id: i + 1, items: [], name: `MC ${i + 1}` }));
+
+    const fetchMock = vi.spyOn(window, 'fetch').mockImplementation(async (input) => {
+      const url = new URL(String(input), 'http://localhost');
+      const pageNum = Number(url.searchParams.get('pageNum') ?? '0');
+      const pageSize = Number(url.searchParams.get('pageSize') ?? String(cap));
+      const start = pageNum * pageSize;
+      return jsonResponse({ page: all.slice(start, start + pageSize), totalCount: total });
+    });
+
+    const result = await loadAllPages(getMultiCollections);
+
+    expect(fetchMock).toHaveBeenCalledTimes(3);
+    expect(result.complete).toBe(true);
+
+    const requestedUrls = fetchMock.mock.calls.map((call) => new URL(String(call[0]), 'http://localhost'));
+    expect(requestedUrls.map((url) => url.pathname)).toEqual([
+      '/api/v1/multi-collections',
+      '/api/v1/multi-collections',
+      '/api/v1/multi-collections'
+    ]);
+    expect(requestedUrls.map((url) => [url.searchParams.get('pageNum'), url.searchParams.get('pageSize')])).toEqual([
+      ['0', '100'],
+      ['1', '100'],
+      ['2', '100']
+    ]);
+
+    // Pin the exact ids/names returned, including the two page boundaries (index 99/100, 199/200).
+    expect(result.items.map((entry) => entry.id)).toEqual(Array.from({ length: total }, (_, i) => i + 1));
+    expect(result.items[99].name).toBe('MC 100');
+    expect(result.items[100].name).toBe('MC 101');
+    expect(result.items[199].name).toBe('MC 200');
+    expect(result.items[200].name).toBe('MC 201');
+    expect(result.items[249].name).toBe('MC 250');
+  });
+
+  it('getMultiCollections: a list at exactly the cap (100) still issues only one request', async () => {
+    const all = Array.from({ length: 100 }, (_, i) => ({ id: i + 1, items: [], name: `MC ${i + 1}` }));
+    const fetchMock = vi.spyOn(window, 'fetch').mockResolvedValue(jsonResponse({ page: all, totalCount: 100 }));
+
+    const result = await loadAllPages(getMultiCollections);
+
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+    expect(result.complete).toBe(true);
+    expect(result.items.map((entry) => entry.id)).toEqual(Array.from({ length: 100 }, (_, i) => i + 1));
+  });
+
+  it('getLibraryBrowseItems: pins the exact merged set across a >cap (150-item) list and threads mediaType into every page', async () => {
+    const total = 150;
+    const cap = 100;
+    const all = Array.from({ length: total }, (_, i) => ({
+      id: i + 1,
+      mediaItemId: i + 1,
+      mediaType: 'Movie' as const,
+      title: `Movie ${i + 1}`
+    }));
+
+    const fetchMock = vi.spyOn(window, 'fetch').mockImplementation(async (input) => {
+      const url = new URL(String(input), 'http://localhost');
+      const pageNum = Number(url.searchParams.get('pageNum') ?? '0');
+      const pageSize = Number(url.searchParams.get('pageSize') ?? String(cap));
+      const start = pageNum * pageSize;
+      return jsonResponse({ page: all.slice(start, start + pageSize), totalCount: total });
+    });
+
+    const result = await loadAllPages(getLibraryBrowseItems, { mediaType: 'Movie' });
+
+    expect(fetchMock).toHaveBeenCalledTimes(2);
+    expect(result.complete).toBe(true);
+
+    const requestedUrls = fetchMock.mock.calls.map((call) => new URL(String(call[0]), 'http://localhost'));
+    expect(
+      requestedUrls.map((url) => [
+        url.searchParams.get('mediaType'),
+        url.searchParams.get('pageNum'),
+        url.searchParams.get('pageSize')
+      ])
+    ).toEqual([
+      ['Movie', '0', '100'],
+      ['Movie', '1', '100']
+    ]);
+
+    // Pin the exact titles across the page boundary at index 99/100.
+    expect(result.items.map((item) => item.title)).toEqual(Array.from({ length: total }, (_, i) => `Movie ${i + 1}`));
+    expect(result.items[99].title).toBe('Movie 100');
+    expect(result.items[100].title).toBe('Movie 101');
+    expect(result.items[149].title).toBe('Movie 150');
+  });
+});
diff --git a/web/src/api/paging.ts b/web/src/api/paging.ts
new file mode 100644
index 000000000..4ae83d20c
--- /dev/null
+++ b/web/src/api/paging.ts
@@ -0,0 +1,107 @@
+/**
+ * Shared client-side paging helper (issue #644, extending the `loadAllRerunCollections` pattern
+ * introduced for SchedulesScreen in #634).
+ *
+ * Paged list endpoints under `/api/v1` clamp `pageSize` server-side (each controller's own
+ * `MaxPageSize`, currently 100 for rerun-collections, multi-collections, and library/browse — see
+ * `RerunCollectionController`/`MultiCollectionController`/`LibraryBrowseController`). Requesting a
+ * `pageSize` above the cap buys nothing: the server silently clamps it, so a single oversized
+ * request only ever returns the first page's worth of rows and the rest vanish with no error and
+ * no truncation indicator.
+ *
+ * A screen that needs the FULL list (not a paginated view) must page to completeness against
+ * `totalCount` instead of inflating `pageSize` — the client pages, the server stays bounded
+ * (the `api.search-allitems-paging` precedent). Use this helper rather than copying the loop.
+ *
+ * **This is only for lists that are bounded by construction** (admin-created collections/rerun
+ * entries/playlists — hundreds of rows at most). It must NOT be used as a picker/typeahead data
+ * source over a media library table (Episode/Song/Image/Movie/MusicVideo can run into the tens of
+ * thousands) — see `docs/decisions/records/spa/list-completeness-vs-bounded-pickers.md` (#644
+ * follow-up review). Those call sites fetch a single bounded page directly and surface the
+ * truncation instead.
+ */
+
+export interface PagedResult<T> {
+  page?: T[] | null;
+  totalCount?: number | null;
+}
+
+/** Matches every generated paged-list params shape (`GetMultiCollectionsParams`, etc). */
+export interface PagingParams {
+  pageNum?: number;
+  pageSize?: number;
+}
+
+export interface LoadAllPagesResult<T> {
+  /**
+   * `false` when the loop stopped before reaching `totalCount` — either because a page came back
+   * empty (defensive break; the totalCount never converged) or because `signal` was aborted
+   * mid-loop. A caller that needs the FULL list must check this rather than trusting `items` to be
+   * complete just because the promise resolved without throwing (#644 follow-up finding F4 — the
+   * old `break` returned a partial list indistinguishable from a complete one, and this is
+   * reachable in normal operation: `GetLibraryBrowseItemsHandler.HydrateMediaItems` drops Lucene
+   * hits whose DB rows have since vanished, and the handler's own comment notes Lucene's
+   * `TotalCount` can be stale).
+   */
+  complete: boolean;
+  items: T[];
+}
+
+type BaseParams<P extends PagingParams> = Omit<P, 'pageNum' | 'pageSize'>;
+
+// `baseParams` is required whenever `P` (minus `pageNum`/`pageSize`) has any required field of its
+// own; it's only optional when every remaining field is optional (an empty-object-assignable
+// type). This has to be encoded as a conditional REST TUPLE, not a `baseParams?: X | never`
+// parameter — marking the parameter itself optional with `?` makes an omitted argument type-check
+// regardless of `X`, which is exactly the hole this is meant to close (#644 follow-up finding F6;
+// the old single-signature `= {} as Omit<P, ...>` default silently defeated the check for every
+// `P`, required fields included).
+// "is an empty object type assignable here" is exactly the "does BaseParams<P> have any required
+// field" check, so the `{}` is intentional.
+// eslint-disable-next-line @typescript-eslint/no-empty-object-type
+type LoadAllPagesArgs<P extends PagingParams> = {} extends BaseParams<P>
+  ? [baseParams?: BaseParams<P>, pageSize?: number, signal?: AbortSignal]
+  : [baseParams: BaseParams<P>, pageSize?: number, signal?: AbortSignal];
+
+/**
+ * Repeatedly calls `fetchPage` with increasing `pageNum` (0-based, per `api.paging-zero-based`)
+ * until the accumulated results reach `totalCount`, or a page comes back empty (defensive break
+ * against a `totalCount` that never converges), or `signal` is aborted. `pageSize` defaults to
+ * 100, the cap shared by every paged `/api/v1` list endpoint today; pass a smaller value only if a
+ * specific endpoint's cap is lower.
+ */
+export async function loadAllPages<T, P extends PagingParams>(
+  fetchPage: (params: P) => Promise<PagedResult<T>>,
+  ...rest: LoadAllPagesArgs<P>
+): Promise<LoadAllPagesResult<T>> {
+  const [baseParams = {} as BaseParams<P>, pageSize = 100, signal] = rest as [BaseParams<P>?, number?, AbortSignal?];
+
+  if (signal?.aborted) {
+    return { complete: false, items: [] };
+  }
+
+  const first = await fetchPage({ ...baseParams, pageNum: 0, pageSize } as P);
+  const items: T[] = first.page ? [...first.page] : [];
+  const totalCount = first.totalCount ?? items.length;
+  let pageNum = 1;
+
+  while (items.length < totalCount) {
+    if (signal?.aborted) {
+      return { complete: false, items };
+    }
+
+    const next = await fetchPage({ ...baseParams, pageNum, pageSize } as P);
+    const nextPage = next.page ?? [];
+
+    if (nextPage.length === 0) {
+      return { complete: false, items };
+    }
+
+    // Push in place rather than `[...items, ...nextPage]` (#644 follow-up finding F7) — the spread
+    // form reallocates and copies the whole accumulator on every page, making a long list O(n²).
+    items.push(...nextPage);
+    pageNum += 1;
+  }
+
+  return { complete: true, items };
+}
diff --git a/web/src/components/forms.tsx b/web/src/components/forms.tsx
index 834f37388..569d1e0d6 100644
--- a/web/src/components/forms.tsx
+++ b/web/src/components/forms.tsx
@@ -187,6 +187,10 @@ export interface SelectProps {
   size?: ControlSize;
   fullWidth?: boolean;
   style?: CSSProperties;
+  // Associates an out-of-band hint (e.g. a truncation message rendered as a sibling) with this
+  // control for screen readers, matching how `error`/`help` text is otherwise co-located with a
+  // field. Pass the id of the element carrying the hint text.
+  ariaDescribedBy?: string;
 }
 
 export function Select({
@@ -197,7 +201,8 @@ export function Select({
   disabled = false,
   size = 'md',
   fullWidth = true,
-  style
+  style,
+  ariaDescribedBy
 }: SelectProps) {
   const normalizedOptions = options.map((option) =>
     typeof option === 'string' ? { value: option, label: option } : option
@@ -215,7 +220,13 @@ export function Select({
         )}
         style={style}
       >
-        <select className="ctv-select" value={value} onChange={onChange} disabled={disabled}>
+        <select
+          aria-describedby={ariaDescribedBy}
+          className="ctv-select"
+          value={value}
+          onChange={onChange}
+          disabled={disabled}
+        >
           {normalizedOptions.map((option) => (
             <option key={option.value} value={option.value}>
               {option.label}
diff --git a/web/src/schedules/ScheduleItemInspector.tsx b/web/src/schedules/ScheduleItemInspector.tsx
index 9959a9aff..53dfc0b84 100644
--- a/web/src/schedules/ScheduleItemInspector.tsx
+++ b/web/src/schedules/ScheduleItemInspector.tsx
@@ -368,6 +368,13 @@ function SourcePicker({
   }
 
   if (type === 'RerunFirstRun' || type === 'RerunRerun') {
+    // Out-of-list injection (round-3 review F2): the picker source is a Class A `loadAllPages`
+    // loop (SchedulesScreen.loadAllRerunCollections) that can legitimately return an incomplete
+    // page set, so the item's stored rerunCollectionId may not be among `pickers.rerunCollections`
+    // — mirrors RerunCollectionsScreen's and PlaylistsScreen's `selectedInList` prepend.
+    const rerunSelectedInList =
+      item.rerunCollectionId != null && pickers.rerunCollections.some((c) => c.id === item.rerunCollectionId);
+
     return (
       <Select
         label="Rerun collection"
@@ -377,7 +384,13 @@ function SourcePicker({
           const name = pickers.rerunCollections.find((c) => c.id === id)?.name ?? null;
           onChange({ ...item, rerunCollectionId: id, rerunCollectionName: name });
         }}
-        options={[{ value: '', label: '(none)' }, ...pickers.rerunCollections.map((c) => ({ value: `${c.id}`, label: c.name ?? `Rerun ${c.id}` }))]}
+        options={[
+          { value: '', label: '(none)' },
+          ...(item.rerunCollectionId != null && !rerunSelectedInList
+            ? [{ value: `${item.rerunCollectionId}`, label: item.rerunCollectionName || `Rerun ${item.rerunCollectionId}` }]
+            : []),
+          ...pickers.rerunCollections.map((c) => ({ value: `${c.id}`, label: c.name ?? `Rerun ${c.id}` }))
+        ]}
       />
     );
   }
diff --git a/web/src/screens/FillerPresetsScreen.test.tsx b/web/src/screens/FillerPresetsScreen.test.tsx
new file mode 100644
index 000000000..7a1240d5e
--- /dev/null
+++ b/web/src/screens/FillerPresetsScreen.test.tsx
@@ -0,0 +1,159 @@
+import { cleanup, render, screen, waitFor, within } from '@testing-library/react';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { FillerPresetsScreen } from './FillerPresetsScreen';
+
+function jsonResponse(body: unknown, status = 200): Response {
+  return new Response(JSON.stringify(body), {
+    headers: { 'Content-Type': 'application/json' },
+    status
+  });
+}
+
+const presetList = [{ fillerKind: 'PreRoll', id: 1, name: 'Bumper' }];
+
+// Editing this preset: collectionType 'TelevisionShow', mediaItemId 9999 — deliberately NOT among
+// the library-browse page below, to exercise the F2 out-of-list injection. (FillerPresetsScreen's
+// COLLECTION_TYPES doesn't offer a raw 'Movie' entry — TelevisionShow/TelevisionSeason/Artist are
+// its media-item-backed types.)
+const editPreset = {
+  allowWatermarks: false,
+  collectionId: null,
+  collectionType: 'TelevisionShow',
+  count: 3,
+  duration: null,
+  expression: null,
+  fillerKind: 'PreRoll',
+  fillerMode: 'Count',
+  id: 1,
+  mediaItemId: 9999,
+  multiCollectionId: null,
+  name: 'Bumper',
+  padToNearestMinute: null,
+  playlistId: null,
+  smartCollectionId: null,
+  useChaptersAsMediaItems: false
+};
+
+// One bounded page (cap 100) of browse items, none of which is id 9999. Every id-ish field is
+// populated (not just mediaItemId) so the fixture works regardless of which COLLECTION_TYPES
+// entry's `itemId` extractor is in play (Collection reads collectionId, Movie reads mediaItemId).
+function browsePage(count: number, totalCount: number) {
+  return {
+    page: Array.from({ length: count }, (_, i) => ({
+      collectionId: i + 1,
+      id: i + 1,
+      mediaItemId: i + 1,
+      mediaType: 'Movie' as const,
+      multiCollectionId: i + 1,
+      smartCollectionId: i + 1,
+      title: `Movie ${i + 1}`
+    })),
+    totalCount
+  };
+}
+
+interface MockOptions {
+  browseCount?: number;
+  browseTotal?: number;
+  onRequest?: (url: string, method: string, body: unknown) => Response | null;
+}
+
+function mockApi(options: MockOptions = {}) {
+  const browseCount = options.browseCount ?? 3;
+  const browseTotal = options.browseTotal ?? 3;
+
+  return vi.spyOn(window, 'fetch').mockImplementation((input: RequestInfo | URL, init?: RequestInit) => {
+    const url = new URL(input.toString(), 'http://localhost');
+    const pathname = url.pathname;
+    const method = (init?.method ?? 'GET').toUpperCase();
+    const body = init?.body ? JSON.parse(String(init.body)) : undefined;
+
+    if (options.onRequest) {
+      const override = options.onRequest(input.toString(), method, body);
+      if (override) {
+        return Promise.resolve(override);
+      }
+    }
+
+    if (pathname === '/api/v1/filler-presets' && method === 'GET') {
+      return Promise.resolve(jsonResponse(presetList));
+    }
+
+    if (pathname === '/api/v1/filler-presets/1' && method === 'GET') {
+      return Promise.resolve(jsonResponse(editPreset));
+    }
+
+    if (pathname === '/api/v1/library/browse' && method === 'GET') {
+      return Promise.resolve(jsonResponse(browsePage(browseCount, browseTotal)));
+    }
+
+    return Promise.resolve(new Response(null, { status: 204 }));
+  });
+}
+
+describe('FillerPresetsScreen', () => {
+  afterEach(() => {
+    cleanup();
+    vi.restoreAllMocks();
+    window.history.pushState({}, '', '/app/filler-presets');
+  });
+
+  beforeEach(() => {
+    window.localStorage.clear();
+    window.history.pushState({}, '', '/app/filler-presets');
+  });
+
+  it('renders the filler preset list', async () => {
+    mockApi();
+    render(<FillerPresetsScreen />);
+
+    expect(await screen.findByText('Bumper')).toBeInTheDocument();
+  });
+
+  it('Class B picker: the default Collection-type picker issues exactly ONE /library/browse request (#644 follow-up)', async () => {
+    window.history.pushState({}, '', '/app/filler-presets/add');
+    const fetchMock = mockApi();
+    render(<FillerPresetsScreen />);
+
+    // Default draft collectionType is 'Collection'; wait for its picker to finish loading.
+    await screen.findByText('Movie 1');
+
+    const browseCalls = fetchMock.mock.calls.filter(
+      ([u]) => new URL(u.toString(), 'http://localhost').pathname === '/api/v1/library/browse'
+    );
+    expect(browseCalls).toHaveLength(1);
+  });
+
+  it('shows the truncation hint when totalCount exceeds the loaded page, and hides it when it does not', async () => {
+    window.history.pushState({}, '', '/app/filler-presets/add');
+    mockApi({ browseCount: 100, browseTotal: 250 });
+    render(<FillerPresetsScreen />);
+
+    expect(await screen.findByText('Showing the first 100 of 250 — use search to narrow.')).toBeInTheDocument();
+
+    cleanup();
+
+    window.history.pushState({}, '', '/app/filler-presets/add');
+    mockApi({ browseCount: 50, browseTotal: 50 });
+    render(<FillerPresetsScreen />);
+
+    await screen.findByText('Movie 1');
+    expect(screen.queryByText(/Showing the first/)).not.toBeInTheDocument();
+  });
+
+  it('F2: injects the out-of-list current selection so an id outside the loaded page still renders as selected', async () => {
+    window.history.pushState({}, '', '/app/filler-presets/1');
+    mockApi();
+    render(<FillerPresetsScreen />);
+
+    await waitFor(() => expect(screen.getByDisplayValue('Bumper')).toBeInTheDocument());
+
+    // Select order: Kind, Mode, Pad to nearest minute, Collection type, then the activeConfig
+    // ("Movie") picker last — it shows the out-of-list #9999 option, selected, never falling back
+    // to "(none)" even though 9999 isn't in the 3-item loaded page.
+    const comboboxes = await screen.findAllByRole('combobox');
+    const pickerSelect = comboboxes[comboboxes.length - 1];
+    expect((pickerSelect as HTMLSelectElement).value).toBe('9999');
+    expect(within(pickerSelect).getByText('#9999')).toBeInTheDocument();
+  });
+});
diff --git a/web/src/screens/FillerPresetsScreen.tsx b/web/src/screens/FillerPresetsScreen.tsx
index 85858d8ac..c466a60cd 100644
--- a/web/src/screens/FillerPresetsScreen.tsx
+++ b/web/src/screens/FillerPresetsScreen.tsx
@@ -19,6 +19,14 @@ import {
 
 const BASE_PATH = '/app/filler-presets';
 
+// Class B picker (#644 follow-up): the filler-preset collection-type picker browses the largest
+// media-library tables (Episode, Song, Image, Movie, MusicVideo, ...), which can run into the tens
+// of thousands of rows. Paging to completeness would mean ~200 serial requests — each more
+// expensive than the last (LuceneSearchIndex.Search computes hitsLimit = skip + limit) — to
+// populate a native <select> with thousands of <option> nodes. Load ONE bounded page instead and
+// surface the truncation (see docs/decisions/records/spa/list-completeness-vs-bounded-pickers.md).
+const LIBRARY_BROWSE_PAGE_CAP = 100;
+
 type Draft = CreateFillerPresetRequest;
 type FillerKind = Draft['fillerKind'];
 type FillerMode = Draft['fillerMode'];
@@ -444,6 +452,8 @@ function FillerEditor({ mode }: { mode: { id: number; kind: 'edit' } | { kind: '
   const [saving, setSaving] = useState(false);
   const [pickerItems, setPickerItems] = useState<LibraryBrowseItem[]>([]);
   const [pickerError, setPickerError] = useState<null | string>(null);
+  const [pickerTruncated, setPickerTruncated] = useState(false);
+  const [pickerTotalCount, setPickerTotalCount] = useState<null | number>(null);
 
   const isEdit = mode.kind === 'edit';
 
@@ -486,17 +496,25 @@ function FillerEditor({ mode }: { mode: { id: number; kind: 'edit' } | { kind: '
 
     let active = true;
 
-    getLibraryBrowseItems({ mediaType: config.browse, pageSize: 500 })
+    // Class B (#644 follow-up) — load ONE bounded page rather than paging to completeness; see the
+    // module-level comment on LIBRARY_BROWSE_PAGE_CAP.
+    getLibraryBrowseItems({ mediaType: config.browse, pageNum: 0, pageSize: LIBRARY_BROWSE_PAGE_CAP })
       .then((result) => {
         if (active) {
-          setPickerItems(result.page ?? []);
+          const page = result.page ?? [];
+          const totalCount = result.totalCount ?? page.length;
+          setPickerItems(page);
           setPickerError(null);
+          setPickerTruncated(totalCount > page.length);
+          setPickerTotalCount(totalCount);
         }
       })
       .catch((error: unknown) => {
         if (active) {
           setPickerItems([]);
           setPickerError(messageFromFillerPresetError(error, 'Unable to load picker items'));
+          setPickerTruncated(false);
+          setPickerTotalCount(null);
         }
       });
 
@@ -559,14 +577,31 @@ function FillerEditor({ mode }: { mode: { id: number; kind: 'edit' } | { kind: '
   };
 
   const pickerValue = activeConfig ? String((draft[activeConfig.field] as null | number) ?? '') : '';
+  const pickerSelectedId = activeConfig ? (draft[activeConfig.field] as null | number) : null;
+  const pickerSelectedInList =
+    pickerSelectedId != null &&
+    pickerItems.some((item) => activeConfig?.itemId(item) === pickerSelectedId);
+  // Out-of-list injection (round-3 review F2): the Class B picker loads only ONE bounded page
+  // (LIBRARY_BROWSE_PAGE_CAP), so a preset whose stored id sits outside that page would otherwise
+  // render as "(none)" while the draft still holds the id — mirrors RerunCollectionsScreen's and
+  // PlaylistsScreen's `selectedInList` prepend.
   const pickerOptions = [
     { label: '(none)', value: '' },
+    ...(pickerSelectedId != null && !pickerSelectedInList
+      ? [{ label: `#${pickerSelectedId}`, value: String(pickerSelectedId) }]
+      : []),
     ...pickerItems.flatMap((item) => {
       const id = activeConfig?.itemId(item);
       return id == null ? [] : [{ label: item.title ?? `#${id}`, value: String(id) }];
     })
   ];
 
+  const pickerHelp = pickerError
+    ? pickerError
+    : pickerTruncated
+      ? `Showing the first ${pickerItems.length} of ${pickerTotalCount} — use search to narrow.`
+      : undefined;
+
   const collectionTypeOptions = COLLECTION_TYPES.filter(
     (entry) => !entry.playlistOnly || (draft.fillerKind !== 'Fallback' && draft.fillerKind !== 'Tail')
   ).map((entry) => ({ label: entry.label, value: entry.value }));
@@ -703,7 +738,7 @@ function FillerEditor({ mode }: { mode: { id: number; kind: 'edit' } | { kind: '
           />
         </Row>
         {activeConfig && (
-          <Row control={360} help={pickerError ?? undefined} label={activeConfig.label}>
+          <Row control={360} help={pickerHelp} label={activeConfig.label}>
             <Select
               onChange={(event) =>
                 set({ [activeConfig.field]: event.target.value === '' ? null : Number(event.target.value) })
diff --git a/web/src/screens/MultiCollectionsScreen.test.tsx b/web/src/screens/MultiCollectionsScreen.test.tsx
index cf4ab1e3d..c3008345e 100644
--- a/web/src/screens/MultiCollectionsScreen.test.tsx
+++ b/web/src/screens/MultiCollectionsScreen.test.tsx
@@ -281,6 +281,35 @@ describe('MultiCollectionsScreen', () => {
     expect((screen.getByLabelText('Weight for Action') as HTMLInputElement).value).toBe('1');
   });
 
+  it('pages to completeness: a >100-item list issues a SECOND request and renders every row (#644 follow-up)', async () => {
+    // Unlike `mockApi`, this responds according to the requested pageNum/pageSize — pinning that the
+    // SCREEN itself (not just the `loadAllPages` helper in isolation) actually issues a second
+    // request rather than silently truncating to the server's first-page cap.
+    const total = 120;
+    const cap = 100;
+    const all = Array.from({ length: total }, (_, i) => ({ id: i + 1, items: [], name: `MC ${i + 1}` }));
+
+    const fetchMock = vi.spyOn(window, 'fetch').mockImplementation((input: RequestInfo | URL) => {
+      const url = new URL(input.toString(), 'http://localhost');
+      if (url.pathname === '/api/v1/multi-collections') {
+        const pageNum = Number(url.searchParams.get('pageNum') ?? '0');
+        const pageSize = Number(url.searchParams.get('pageSize') ?? String(cap));
+        const start = pageNum * pageSize;
+        return Promise.resolve(jsonResponse({ page: all.slice(start, start + pageSize), totalCount: total }));
+      }
+      return Promise.resolve(new Response(null, { status: 204 }));
+    });
+
+    render(<MultiCollectionsScreen />);
+
+    expect(await screen.findByText('MC 120')).toBeInTheDocument();
+    expect(screen.getByText('MC 1')).toBeInTheDocument();
+    expect(screen.getByText(`${total} multi-collections`)).toBeInTheDocument();
+
+    const listCalls = fetchMock.mock.calls.filter(([u]) => new URL(u.toString(), 'http://localhost').pathname === '/api/v1/multi-collections');
+    expect(listCalls).toHaveLength(2);
+  });
+
   it('confirms and DELETEs a multi-collection', async () => {
     const fetchMock = mockApi();
 
diff --git a/web/src/screens/MultiCollectionsScreen.tsx b/web/src/screens/MultiCollectionsScreen.tsx
index d0ff0360d..e9fcfa903 100644
--- a/web/src/screens/MultiCollectionsScreen.tsx
+++ b/web/src/screens/MultiCollectionsScreen.tsx
@@ -10,6 +10,7 @@ import {
   getMultiCollectionWithMeta,
   getMultiCollections,
   getSmartCollections,
+  loadAllPages,
   messageFromMultiCollectionError,
   updateMultiCollection,
   type MediaCollection,
@@ -21,30 +22,46 @@ import {
 /* ---------- data hook ---------- */
 
 type ListState =
-  | { data: MultiCollection[]; error: null; status: 'success' }
+  | { data: MultiCollection[]; error: null; incomplete: boolean; status: 'success' }
   | { data: null; error: string; status: 'error' }
   | { data: null; error: null; status: 'loading' };
 
 function useMultiCollectionsData() {
   const [state, setState] = useState<ListState>({ data: null, error: null, status: 'loading' });
   const activeRef = useRef(true);
+  // Monotonic request id (spa-conventions §3): `refresh()` is reachable repeatedly (delete/save),
+  // and now that a load is a multi-request `loadAllPages` loop, an older loop can resolve after a
+  // newer one — guarding on `activeRef` (still mounted) alone isn't enough (#644 follow-up F3).
+  const seqRef = useRef(0);
+  const abortRef = useRef<AbortController | null>(null);
 
   useEffect(() => {
     activeRef.current = true;
     return () => {
       activeRef.current = false;
+      abortRef.current?.abort();
     };
   }, []);
 
   const load = useCallback(() => {
-    getMultiCollections({ pageSize: 1000 })
-      .then((result) => {
-        if (activeRef.current) {
-          setState({ data: result.page ?? [], error: null, status: 'success' });
+    abortRef.current?.abort();
+    const controller = new AbortController();
+    abortRef.current = controller;
+    const seq = (seqRef.current += 1);
+
+    loadAllPages(getMultiCollections, undefined, undefined, controller.signal)
+      .then(({ complete, items }) => {
+        if (activeRef.current && seqRef.current === seq) {
+          if (!complete) {
+            // #644 follow-up F4: a partial result is otherwise indistinguishable from a complete
+            // one. Surfaced via `incomplete` below; also logged so it shows up outside the UI.
+            console.warn('MultiCollectionsScreen: multi-collections list load did not complete; some items may be missing');
+          }
+          setState({ data: items, error: null, incomplete: !complete, status: 'success' });
         }
       })
       .catch((error: unknown) => {
-        if (activeRef.current) {
+        if (activeRef.current && seqRef.current === seq) {
           setState({ data: null, error: messageFromMultiCollectionError(error), status: 'error' });
         }
       });
@@ -546,6 +563,9 @@ export function MultiCollectionsScreen() {
     <div className="ctv-collections">
       <div className="ctv-channels-actionbar">
         <Badge tone="neutral">{multiCollections.length} multi-collections</Badge>
+        {state.incomplete && (
+          <Badge tone="warn">List may be incomplete — retry to reload</Badge>
+        )}
         <span className="ctv-channels-spacer" />
         <Button onClick={() => setEditing({ kind: 'new' })} size="sm" startIcon={<Plus aria-hidden="true" size={14} />}>
           New multi-collection
diff --git a/web/src/screens/PlaylistsScreen.tsx b/web/src/screens/PlaylistsScreen.tsx
index dd0f7fdc6..4217dfcd9 100644
--- a/web/src/screens/PlaylistsScreen.tsx
+++ b/web/src/screens/PlaylistsScreen.tsx
@@ -1,4 +1,4 @@
-import { useCallback, useEffect, useRef, useState } from 'react';
+import { useCallback, useEffect, useId, useRef, useState } from 'react';
 import {
   ArrowDown,
   ArrowLeft,
@@ -31,6 +31,7 @@ import {
   getPlaylistItemsWithMeta,
   getPlaylists,
   getSmartCollections,
+  loadAllPages,
   messageFromPlaylistError,
   previewPlaylist,
   updatePlaylist,
@@ -51,6 +52,22 @@ interface PickerOption {
   name: string;
 }
 
+// #644 follow-up: `browse` (media-library) picker sources are Class B — bounded to one page, with
+// `hint: 'truncated'`/`totalCount` telling the caller there's more than fits (a real, expected
+// cap — narrow via search). `collection`/`multi`/`smart` sources stay Class A (page to
+// completeness) since they're inherently small, admin-created lists; `hint: 'incomplete'` there
+// instead reflects `loadAllPages`'s `complete` flag, i.e. a defensive load that did not converge,
+// not a cap. These two are NOT the same condition and must render different copy (round-3 review
+// F1): "showing the first N of M" is arithmetically vacuous — and points at a search box that
+// doesn't exist for this picker — when N === M on an incomplete Class A load.
+interface PickerLoadResult {
+  items: PickerOption[];
+  totalCount: number | null;
+  hint: 'incomplete' | 'none' | 'truncated';
+}
+
+const LIBRARY_BROWSE_PAGE_CAP = 100;
+
 // The 12 playlist item types (mirrors PlaylistEditor.razor's Collection Type select).
 // Playlist / RemoteStream and the rerun-only types are intentionally excluded here.
 // Each entry knows how to load its picker options; every media-item type maps to a
@@ -139,24 +156,47 @@ function orderOptionsWithCurrent(type: CollectionType, current: PlaybackOrder):
   return options.some((option) => option.value === current) ? options : [...options, orderOption(current)];
 }
 
-function loadPickerOptions(type: CollectionType): Promise<PickerOption[]> {
+function loadPickerOptions(type: CollectionType, signal?: AbortSignal): Promise<PickerLoadResult> {
   const config = configFor(type);
   if (!config) {
-    return Promise.resolve([]);
+    return Promise.resolve({ hint: 'none', items: [], totalCount: 0 });
   }
 
   switch (config.source) {
     case 'collection':
-      return getCollections().then((list) => list.map((entry) => ({ id: entry.id, name: entry.name ?? `#${entry.id}` })));
+      return getCollections().then((list) => {
+        const items = list.map((entry) => ({ id: entry.id, name: entry.name ?? `#${entry.id}` }));
+        return { hint: 'none' as const, items, totalCount: items.length };
+      });
     case 'multi':
-      return getMultiCollections({ pageSize: 1000 }).then((result) =>
-        (result.page ?? []).map((entry) => ({ id: entry.id, name: entry.name ?? `#${entry.id}` }))
-      );
+      return loadAllPages(getMultiCollections, undefined, undefined, signal).then(({ complete, items: list }) => {
+        const items = list.map((entry) => ({ id: entry.id, name: entry.name ?? `#${entry.id}` }));
+        if (!complete && !signal?.aborted) {
+          // #644 follow-up F3: a superseded/aborted load (a type switch mid-load) also returns
+          // `complete: false` — that's expected, not a defect, so don't warn on it.
+          console.warn('PlaylistsScreen: multi-collection picker load did not complete; some items may be missing');
+        }
+        return { hint: complete ? ('none' as const) : ('incomplete' as const), items, totalCount: items.length };
+      });
     case 'smart':
-      return getSmartCollections().then((list) => list.map((entry) => ({ id: entry.id, name: entry.name ?? `#${entry.id}` })));
+      return getSmartCollections().then((list) => {
+        const items = list.map((entry) => ({ id: entry.id, name: entry.name ?? `#${entry.id}` }));
+        return { hint: 'none' as const, items, totalCount: items.length };
+      });
     default:
-      return getLibraryBrowseItems({ mediaType: config.browse, pageSize: 500 }).then((result) =>
-        (result.page ?? []).map((item) => ({ id: item.mediaItemId ?? item.id, name: item.title ?? `#${item.id}` }))
+      // Class B (#644 follow-up): a media-library picker over the largest tables (Episode, Song,
+      // Image, Movie, MusicVideo, ...), which can run into the tens of thousands of rows. Paging to
+      // completeness here would mean ~200 serial requests — each more expensive than the last
+      // (LuceneSearchIndex.Search computes hitsLimit = skip + limit) — to populate a native <select>
+      // with thousands of <option> nodes. Load ONE bounded page instead and surface the truncation
+      // (see docs/decisions/records/spa/list-completeness-vs-bounded-pickers.md).
+      return getLibraryBrowseItems({ mediaType: config.browse, pageNum: 0, pageSize: LIBRARY_BROWSE_PAGE_CAP }).then(
+        (result) => {
+          const page = result.page ?? [];
+          const items = page.map((item) => ({ id: item.mediaItemId ?? item.id, name: item.title ?? `#${item.id}` }));
+          const totalCount = result.totalCount ?? items.length;
+          return { hint: totalCount > items.length ? ('truncated' as const) : ('none' as const), items, totalCount };
+        }
       );
   }
 }
@@ -375,6 +415,9 @@ function PlaylistEditor({ playlistId, onBack, onSaved }: { playlistId: number; o
   const [selectedKey, setSelectedKey] = useState<string | null>(null);
   const [pickerItems, setPickerItems] = useState<PickerOption[]>([]);
   const [pickerError, setPickerError] = useState<string | null>(null);
+  const [pickerHint, setPickerHint] = useState<PickerLoadResult['hint']>('none');
+  const [pickerTotalCount, setPickerTotalCount] = useState<number | null>(null);
+  const pickerHelpId = useId();
   const [saving, setSaving] = useState(false);
   const [saveError, setSaveError] = useState<string | null>(null);
   const [previewItems, setPreviewItems] = useState<PlaylistPreviewItem[] | null>(null);
@@ -426,29 +469,36 @@ function PlaylistEditor({ playlistId, onBack, onSaved }: { playlistId: number; o
   const selectedType = selectedItem?.collectionType;
   const isSystem = state.status === 'ready' && state.playlist.isSystem;
 
-  // Load the picker list for the selected item's type. Reset only in the async callbacks.
+  // Load the picker list for the selected item's type. Reset only in the async callbacks. Uses an
+  // AbortController so switching type mid-load (a Class A `loadAllPages` loop, e.g.
+  // multi-collections) stops issuing further requests rather than just discarding the eventual
+  // result (#644 follow-up F2).
   useEffect(() => {
     if (selectedType === undefined) {
       return;
     }
 
-    let active = true;
-    loadPickerOptions(selectedType)
-      .then((options) => {
-        if (active) {
-          setPickerItems(options);
+    const controller = new AbortController();
+    loadPickerOptions(selectedType, controller.signal)
+      .then(({ hint, items, totalCount }) => {
+        if (!controller.signal.aborted) {
+          setPickerItems(items);
           setPickerError(null);
+          setPickerHint(hint);
+          setPickerTotalCount(totalCount);
         }
       })
       .catch((error: unknown) => {
-        if (active) {
+        if (!controller.signal.aborted) {
           setPickerItems([]);
           setPickerError(messageFromPlaylistError(error, 'Unable to load picker items'));
+          setPickerHint('none');
+          setPickerTotalCount(null);
         }
       });
 
     return () => {
-      active = false;
+      controller.abort();
     };
   }, [selectedType]);
 
@@ -730,16 +780,27 @@ function PlaylistEditor({ playlistId, onBack, onSaved }: { playlistId: number; o
 
           <div style={{ marginTop: 12 }}>
             <Select
+              ariaDescribedBy={pickerError || pickerHint !== 'none' ? pickerHelpId : undefined}
               label={activeConfig?.label ?? 'Selection'}
               onChange={(event) => setItemSelection(selectedItem.key, event.target.value)}
               options={pickerOptions}
               value={selectedItem.selectedId == null ? '' : String(selectedItem.selectedId)}
             />
             {pickerError && (
-              <span className="ctv-field-error" role="alert">
+              <span className="ctv-field-error" id={pickerHelpId} role="alert">
                 {pickerError}
               </span>
             )}
+            {!pickerError && pickerHint === 'truncated' && (
+              <span className="ctv-field-help" id={pickerHelpId}>
+                Showing the first {pickerItems.length} of {pickerTotalCount} — use search to narrow.
+              </span>
+            )}
+            {!pickerError && pickerHint === 'incomplete' && (
+              <span className="ctv-field-help" id={pickerHelpId}>
+                List may be incomplete — retry to reload.
+              </span>
+            )}
           </div>
 
           <div style={{ marginTop: 12 }}>
diff --git a/web/src/screens/RerunCollectionsScreen.test.tsx b/web/src/screens/RerunCollectionsScreen.test.tsx
index 78490ff4c..7f4727e71 100644
--- a/web/src/screens/RerunCollectionsScreen.test.tsx
+++ b/web/src/screens/RerunCollectionsScreen.test.tsx
@@ -162,6 +162,57 @@ describe('RerunCollectionsScreen', () => {
     expect(await within(refreshed[1]).findByText('Bundle')).toBeInTheDocument();
   });
 
+  it('Class B picker: a media-library type issues exactly ONE /library/browse request and surfaces the truncation hint (#644 follow-up)', async () => {
+    const total = 5000;
+    const cap = 100;
+    const page = Array.from({ length: cap }, (_, i) => ({
+      id: i + 1,
+      mediaItemId: i + 1,
+      mediaType: 'Movie' as const,
+      title: `Movie ${i + 1}`
+    }));
+
+    const fetchMock = mockApi({ list: [] });
+    fetchMock.mockImplementation((input: RequestInfo | URL, init?: RequestInit) => {
+      const url = new URL(input.toString(), 'http://localhost');
+      const method = (init?.method ?? 'GET').toUpperCase();
+
+      if (url.pathname === '/api/v1/library/browse' && method === 'GET') {
+        return Promise.resolve(jsonResponse({ page, totalCount: total }));
+      }
+      if (url.pathname === '/api/v1/rerun-collections' && method === 'GET') {
+        return Promise.resolve(jsonResponse({ page: [], totalCount: 0 }));
+      }
+      if (url.pathname === '/api/v1/collections' && method === 'GET') {
+        return Promise.resolve(jsonResponse(manualCollections));
+      }
+      if (url.pathname === '/api/v1/multi-collections' && method === 'GET') {
+        return Promise.resolve(jsonResponse({ page: multiCollections, totalCount: multiCollections.length }));
+      }
+      if (url.pathname === '/api/v1/smart-collections' && method === 'GET') {
+        return Promise.resolve(jsonResponse([]));
+      }
+      return Promise.resolve(new Response(null, { status: 204 }));
+    });
+
+    render(<RerunCollectionsScreen />);
+    fireEvent.click(await screen.findByRole('button', { name: 'New rerun collection' }));
+
+    const typeSelect = (await screen.findAllByRole('combobox'))[0];
+    fireEvent.change(typeSelect, { target: { value: 'Movie' } });
+
+    // The bounded page renders (100 options) and the truncation hint appears.
+    expect(await screen.findByText(/Showing the first 100 of 5000/)).toBeInTheDocument();
+    const picker = (await screen.findAllByRole('combobox'))[1];
+    expect(await within(picker).findByText('Movie 100')).toBeInTheDocument();
+
+    // Exactly ONE /library/browse request — no paging-to-completeness loop over the media library.
+    const browseCalls = fetchMock.mock.calls.filter(
+      ([u]) => new URL(u.toString(), 'http://localhost').pathname === '/api/v1/library/browse'
+    );
+    expect(browseCalls).toHaveLength(1);
+  });
+
   it('preserves an out-of-set stored playback order on edit-load and re-saves it unchanged', async () => {
     const outOfSet = [
       {
@@ -214,6 +265,100 @@ describe('RerunCollectionsScreen', () => {
     });
   });
 
+  it('renders the "List may be incomplete" badge when the rerun-collections load does not complete (round-3 review)', async () => {
+    let callCount = 0;
+
+    vi.spyOn(window, 'fetch').mockImplementation((input: RequestInfo | URL, init?: RequestInit) => {
+      const url = new URL(input.toString(), 'http://localhost');
+      const method = (init?.method ?? 'GET').toUpperCase();
+
+      if (url.pathname === '/api/v1/rerun-collections' && method === 'GET') {
+        callCount += 1;
+        // First page reports totalCount 2 but only returns 1 item; the second page (pageNum=1)
+        // then comes back EMPTY, which loadAllPages treats as a defensive break: `complete: false`.
+        if (callCount === 1) {
+          return Promise.resolve(jsonResponse({ page: [rerunCollections[0]], totalCount: 2 }));
+        }
+        return Promise.resolve(jsonResponse({ page: [], totalCount: 2 }));
+      }
+
+      return Promise.resolve(new Response(null, { status: 204 }));
+    });
+
+    render(<RerunCollectionsScreen />);
+
+    expect(await screen.findByText('List may be incomplete — retry to reload')).toBeInTheDocument();
+    expect(callCount).toBe(2);
+  });
+
+  it('screen-level: an older overlapping refresh must NOT overwrite a newer one (seqRef guard, round-3 review)', async () => {
+    const itemA = { ...rerunCollections[0], id: 101, name: 'Item A' };
+    const itemB = { ...rerunCollections[0], id: 102, name: 'Item B' };
+    const staleAfterA = { ...rerunCollections[0], id: 201, name: 'Stale After A' };
+    const freshAfterB = { ...rerunCollections[0], id: 202, name: 'Fresh After B' };
+
+    let listCallCount = 0;
+    const staleRelease: { resolve: (() => void) | null } = { resolve: null };
+
+    const fetchMock = vi.spyOn(window, 'fetch').mockImplementation((input: RequestInfo | URL, init?: RequestInit) => {
+      const url = new URL(input.toString(), 'http://localhost');
+      const method = (init?.method ?? 'GET').toUpperCase();
+
+      if (url.pathname === '/api/v1/rerun-collections' && method === 'GET') {
+        listCallCount += 1;
+        // Call 1: initial mount load. Call 2: refresh after deleting A — held pending (the OLDER
+        // overlapping load). Call 3: refresh after deleting B — resolves immediately (the NEWER
+        // load), before call 2 is ever released.
+        if (listCallCount === 1) {
+          return Promise.resolve(jsonResponse({ page: [itemA, itemB], totalCount: 2 }));
+        }
+        if (listCallCount === 2) {
+          return new Promise<Response>((resolve) => {
+            staleRelease.resolve = () => resolve(jsonResponse({ page: [staleAfterA], totalCount: 1 }));
+          });
+        }
+        return Promise.resolve(jsonResponse({ page: [freshAfterB], totalCount: 1 }));
+      }
+
+      if (/^\/api\/v1\/rerun-collections\/\d+$/.test(url.pathname) && method === 'DELETE') {
+        return Promise.resolve(new Response(null, { status: 204 }));
+      }
+
+      return Promise.resolve(new Response(null, { status: 204 }));
+    });
+
+    render(<RerunCollectionsScreen />);
+
+    expect(await screen.findByText('Item A')).toBeInTheDocument();
+    expect(screen.getByText('Item B')).toBeInTheDocument();
+
+    // Delete A -> refresh() issues the OLDER overlapping load (call 2), held pending.
+    const rowA = screen.getByText('Item A').closest('.ctv-settings-flush-row') as HTMLElement;
+    fireEvent.click(within(rowA).getByRole('button', { name: 'Delete' }));
+    fireEvent.click(within(await screen.findByRole('dialog')).getByRole('button', { name: 'Delete' }));
+
+    await waitFor(() => expect(listCallCount).toBe(2));
+    // The pending call 2 hasn't resolved, so the list (and Item B) is still showing.
+    expect(screen.getByText('Item B')).toBeInTheDocument();
+
+    // Delete B -> refresh() issues the NEWER load (call 3), which resolves right away.
+    const rowB = screen.getByText('Item B').closest('.ctv-settings-flush-row') as HTMLElement;
+    fireEvent.click(within(rowB).getByRole('button', { name: 'Delete' }));
+    fireEvent.click(within(await screen.findByRole('dialog')).getByRole('button', { name: 'Delete' }));
+
+    expect(await screen.findByText('Fresh After B')).toBeInTheDocument();
+
+    // Now release the OLDER (call 2) load. Its seq no longer matches seqRef.current, so it must
+    // NOT overwrite the already-rendered newer result.
+    staleRelease.resolve?.();
+    await waitFor(() => expect(fetchMock.mock.calls.length).toBeGreaterThan(0));
+    // Let the resolved (but stale) promise's `.then` run.
+    await new Promise((resolve) => setTimeout(resolve, 0));
+
+    expect(screen.queryByText('Stale After A')).not.toBeInTheDocument();
+    expect(screen.getByText('Fresh After B')).toBeInTheDocument();
+  });
+
   it('confirms and DELETEs a rerun collection', async () => {
     const fetchMock = mockApi();
 
diff --git a/web/src/screens/RerunCollectionsScreen.tsx b/web/src/screens/RerunCollectionsScreen.tsx
index 4fbcf193d..7e3502fdd 100644
--- a/web/src/screens/RerunCollectionsScreen.tsx
+++ b/web/src/screens/RerunCollectionsScreen.tsx
@@ -1,4 +1,4 @@
-import { useCallback, useEffect, useRef, useState } from 'react';
+import { useCallback, useEffect, useId, useRef, useState } from 'react';
 import { ArrowLeft, Check, Plus, Repeat, Trash2, TriangleAlert } from 'lucide-react';
 import { Badge, Button, Card, ConfirmDialog, IconButton, Input, Select, Spinner } from '../components';
 import type { SelectOption } from '../components';
@@ -13,6 +13,7 @@ import {
   getRerunCollectionWithMeta,
   getRerunCollections,
   getSmartCollections,
+  loadAllPages,
   messageFromRerunCollectionError,
   updateRerunCollection,
   type CreateRerunCollectionRequest,
@@ -28,6 +29,22 @@ interface PickerOption {
   name: string;
 }
 
+// #644 follow-up: `browse` (media-library) picker sources are Class B — bounded to one page, with
+// `hint: 'truncated'`/`totalCount` telling the caller there's more than fits (a real, expected
+// cap — narrow via search). `collection`/`multi`/`smart` sources stay Class A (page to
+// completeness) since they're inherently small, admin-created lists; `hint: 'incomplete'` there
+// instead reflects `loadAllPages`'s `complete` flag, i.e. a defensive load that did not converge,
+// not a cap. These two are NOT the same condition and must render different copy (round-3 review
+// F1): "showing the first N of M" is arithmetically vacuous — and points at a search box that
+// doesn't exist for this picker — when N === M on an incomplete Class A load.
+interface PickerLoadResult {
+  items: PickerOption[];
+  totalCount: number | null;
+  hint: 'incomplete' | 'none' | 'truncated';
+}
+
+const LIBRARY_BROWSE_PAGE_CAP = 100;
+
 // The REST-supported selection types (RerunCollectionRequestMapping.IsSupportedSelectionType).
 // Playlist / RerunFirstRun / RerunRerun / SearchQuery / Fake* are intentionally excluded.
 // Each entry knows how to load its picker options; every media-item type maps to a
@@ -92,24 +109,47 @@ function orderOptionsWithCurrent(type: RerunCollectionType, current: PlaybackOrd
   return options.some((option) => option.value === current) ? options : [...options, orderOption(current)];
 }
 
-function loadPickerOptions(type: RerunCollectionType): Promise<PickerOption[]> {
+function loadPickerOptions(type: RerunCollectionType, signal?: AbortSignal): Promise<PickerLoadResult> {
   const config = COLLECTION_TYPES.find((entry) => entry.value === type);
   if (!config) {
-    return Promise.resolve([]);
+    return Promise.resolve({ hint: 'none', items: [], totalCount: 0 });
   }
 
   switch (config.source) {
     case 'collection':
-      return getCollections().then((list) => list.map((entry) => ({ id: entry.id, name: entry.name ?? `#${entry.id}` })));
+      return getCollections().then((list) => {
+        const items = list.map((entry) => ({ id: entry.id, name: entry.name ?? `#${entry.id}` }));
+        return { hint: 'none' as const, items, totalCount: items.length };
+      });
     case 'multi':
-      return getMultiCollections({ pageSize: 1000 }).then((result) =>
-        (result.page ?? []).map((entry) => ({ id: entry.id, name: entry.name ?? `#${entry.id}` }))
-      );
+      return loadAllPages(getMultiCollections, undefined, undefined, signal).then(({ complete, items: list }) => {
+        const items = list.map((entry) => ({ id: entry.id, name: entry.name ?? `#${entry.id}` }));
+        if (!complete && !signal?.aborted) {
+          // #644 follow-up F3: a superseded/aborted load (Retry, or a type switch mid-load) also
+          // returns `complete: false` — that's expected, not a defect, so don't warn on it.
+          console.warn('RerunCollectionsScreen: multi-collection picker load did not complete; some items may be missing');
+        }
+        return { hint: complete ? ('none' as const) : ('incomplete' as const), items, totalCount: items.length };
+      });
     case 'smart':
-      return getSmartCollections().then((list) => list.map((entry) => ({ id: entry.id, name: entry.name ?? `#${entry.id}` })));
+      return getSmartCollections().then((list) => {
+        const items = list.map((entry) => ({ id: entry.id, name: entry.name ?? `#${entry.id}` }));
+        return { hint: 'none' as const, items, totalCount: items.length };
+      });
     default:
-      return getLibraryBrowseItems({ mediaType: config.browse, pageSize: 500 }).then((result) =>
-        (result.page ?? []).map((item) => ({ id: item.mediaItemId ?? item.id, name: item.title ?? `#${item.id}` }))
+      // Class B (#644 follow-up): a media-library picker over the largest tables (Episode, Song,
+      // Image, Movie, MusicVideo, ...), which can run into the tens of thousands of rows. Paging to
+      // completeness here would mean ~200 serial requests — each more expensive than the last
+      // (LuceneSearchIndex.Search computes hitsLimit = skip + limit) — to populate a native <select>
+      // with thousands of <option> nodes. Load ONE bounded page instead and surface the truncation
+      // (see docs/decisions/records/spa/list-completeness-vs-bounded-pickers.md).
+      return getLibraryBrowseItems({ mediaType: config.browse, pageNum: 0, pageSize: LIBRARY_BROWSE_PAGE_CAP }).then(
+        (result) => {
+          const page = result.page ?? [];
+          const items = page.map((item) => ({ id: item.mediaItemId ?? item.id, name: item.title ?? `#${item.id}` }));
+          const totalCount = result.totalCount ?? items.length;
+          return { hint: totalCount > items.length ? ('truncated' as const) : ('none' as const), items, totalCount };
+        }
       );
   }
 }
@@ -117,30 +157,46 @@ function loadPickerOptions(type: RerunCollectionType): Promise<PickerOption[]> {
 /* ---------- data hook ---------- */
 
 type ListState =
-  | { data: RerunCollection[]; error: null; status: 'success' }
+  | { data: RerunCollection[]; error: null; incomplete: boolean; status: 'success' }
   | { data: null; error: string; status: 'error' }
   | { data: null; error: null; status: 'loading' };
 
 function useRerunCollectionsData() {
   const [state, setState] = useState<ListState>({ data: null, error: null, status: 'loading' });
   const activeRef = useRef(true);
+  // Monotonic request id (spa-conventions §3): `refresh()` is reachable repeatedly (delete/save),
+  // and now that a load is a multi-request `loadAllPages` loop, an older loop can resolve after a
+  // newer one — guarding on `activeRef` (still mounted) alone isn't enough (#644 follow-up F3).
+  const seqRef = useRef(0);
+  const abortRef = useRef<AbortController | null>(null);
 
   useEffect(() => {
     activeRef.current = true;
     return () => {
       activeRef.current = false;
+      abortRef.current?.abort();
     };
   }, []);
 
   const load = useCallback(() => {
-    getRerunCollections({ pageSize: 1000 })
-      .then((result) => {
-        if (activeRef.current) {
-          setState({ data: result.page ?? [], error: null, status: 'success' });
+    abortRef.current?.abort();
+    const controller = new AbortController();
+    abortRef.current = controller;
+    const seq = (seqRef.current += 1);
+
+    loadAllPages(getRerunCollections, undefined, undefined, controller.signal)
+      .then(({ complete, items }) => {
+        if (activeRef.current && seqRef.current === seq) {
+          if (!complete) {
+            // #644 follow-up F4: a partial result is otherwise indistinguishable from a complete
+            // one. Surfaced via `incomplete` below; also logged so it shows up outside the UI.
+            console.warn('RerunCollectionsScreen: rerun-collections list load did not complete; some items may be missing');
+          }
+          setState({ data: items, error: null, incomplete: !complete, status: 'success' });
         }
       })
       .catch((error: unknown) => {
-        if (activeRef.current) {
+        if (activeRef.current && seqRef.current === seq) {
           setState({ data: null, error: messageFromRerunCollectionError(error), status: 'error' });
         }
       });
@@ -209,6 +265,9 @@ function RerunCollectionEditor({
   );
   const [pickerItems, setPickerItems] = useState<PickerOption[]>([]);
   const [pickerError, setPickerError] = useState<string | null>(null);
+  const [pickerHint, setPickerHint] = useState<PickerLoadResult['hint']>('none');
+  const [pickerTotalCount, setPickerTotalCount] = useState<number | null>(null);
+  const pickerHelpId = useId();
   const [saveError, setSaveError] = useState<string | null>(null);
   const [saving, setSaving] = useState(false);
   const [conflictOpen, setConflictOpen] = useState(false);
@@ -248,26 +307,32 @@ function RerunCollectionEditor({
   }, [initial, reloadKey]);
 
   // Load the picker list for the active type. Resets only in the async callbacks (never
-  // synchronously in the effect body) per spa-conventions §3.
+  // synchronously in the effect body) per spa-conventions §3. Uses an AbortController so a type
+  // switch mid-load (a Class A `loadAllPages` loop, e.g. multi-collections) stops issuing further
+  // requests rather than just discarding the eventual result (#644 follow-up F2).
   useEffect(() => {
-    let active = true;
+    const controller = new AbortController();
 
-    loadPickerOptions(collectionType)
-      .then((items) => {
-        if (active) {
+    loadPickerOptions(collectionType, controller.signal)
+      .then(({ hint, items, totalCount }) => {
+        if (!controller.signal.aborted) {
           setPickerItems(items);
           setPickerError(null);
+          setPickerHint(hint);
+          setPickerTotalCount(totalCount);
         }
       })
       .catch((error: unknown) => {
-        if (active) {
+        if (!controller.signal.aborted) {
           setPickerItems([]);
           setPickerError(messageFromRerunCollectionError(error, 'Unable to load picker items'));
+          setPickerHint('none');
+          setPickerTotalCount(null);
         }
       });
 
     return () => {
-      active = false;
+      controller.abort();
     };
   }, [collectionType]);
 
@@ -391,16 +456,27 @@ function RerunCollectionEditor({
 
         <div style={{ marginTop: 12 }}>
           <Select
+            ariaDescribedBy={pickerError || pickerHint !== 'none' ? pickerHelpId : undefined}
             label={activeConfig?.label ?? 'Selection'}
             onChange={(event) => setSelected(event.target.value)}
             options={pickerOptions}
             value={draft.selectedId == null ? '' : String(draft.selectedId)}
           />
           {pickerError && (
-            <span className="ctv-field-error" role="alert">
+            <span className="ctv-field-error" id={pickerHelpId} role="alert">
               {pickerError}
             </span>
           )}
+          {!pickerError && pickerHint === 'truncated' && (
+            <span className="ctv-field-help" id={pickerHelpId}>
+              Showing the first {pickerItems.length} of {pickerTotalCount} — use search to narrow.
+            </span>
+          )}
+          {!pickerError && pickerHint === 'incomplete' && (
+            <span className="ctv-field-help" id={pickerHelpId}>
+              List may be incomplete — retry to reload.
+            </span>
+          )}
         </div>
 
         <div style={{ marginTop: 12 }}>
@@ -518,6 +594,9 @@ export function RerunCollectionsScreen() {
     <div className="ctv-collections">
       <div className="ctv-channels-actionbar">
         <Badge tone="neutral">{rerunCollections.length} rerun collections</Badge>
+        {state.incomplete && (
+          <Badge tone="warn">List may be incomplete — retry to reload</Badge>
+        )}
         <span className="ctv-channels-spacer" />
         <Button onClick={() => setEditing({ kind: 'new' })} size="sm" startIcon={<Plus aria-hidden="true" size={14} />}>
           New rerun collection
diff --git a/web/src/screens/SchedulesScreen.tsx b/web/src/screens/SchedulesScreen.tsx
index ab30f1bb8..d25daec4b 100644
--- a/web/src/screens/SchedulesScreen.tsx
+++ b/web/src/screens/SchedulesScreen.tsx
@@ -20,6 +20,7 @@ import {
   getSchedules,
   getGraphicsElements,
   getWatermarks,
+  loadAllPages,
   messageFromScheduleError,
   type ProgramSchedule,
   replaceScheduleItems,
@@ -45,33 +46,24 @@ const DIRTY_PROMPT = 'You have unsaved schedule changes. Discard them?';
 // Server clamps pageSize to MaxPageSize=100 (RerunCollectionController) regardless of what's
 // requested, so a single `pageSize: 1000` request only ever returns the first 100 rows. Page to
 // completeness against totalCount instead of raising the server cap (api.search-allitems-paging
-// precedent — the client pages, the server stays bounded). Mirrors CollectionsScreen.enterReorder.
+// precedent — the client pages, the server stays bounded) via the shared `loadAllPages` helper
+// (`web/src/api/paging.ts`, #644). Mirrors CollectionsScreen.enterReorder.
 //
-// `pageNum` is 0-BASED here and everywhere on /api/v1 (api.paging-zero-based): the first page is 0,
-// so the loop below starts its follow-up requests at 1. Before ersatztv#616 this call site passed
-// `pageNum: 1`, which skipped the first page entirely and showed nothing at all for the ordinary
-// case of <=100 rerun collections — the same call site, one defect earlier.
-const RERUN_PAGE_SIZE = 100;
-
-async function loadAllRerunCollections(): Promise<RerunCollection[]> {
-  const first = await getRerunCollections({ pageNum: 0, pageSize: RERUN_PAGE_SIZE });
-  let all = first.page ?? [];
-  const totalCount = first.totalCount ?? all.length;
-  let pageNum = 1;
-
-  while (all.length < totalCount) {
-    const next = await getRerunCollections({ pageNum, pageSize: RERUN_PAGE_SIZE });
-    const nextPage = next.page ?? [];
-
-    if (nextPage.length === 0) {
-      break;
+// `pageNum` is 0-BASED here and everywhere on /api/v1 (api.paging-zero-based). Before ersatztv#616
+// this call site passed `pageNum: 1`, which skipped the first page entirely and showed nothing at
+// all for the ordinary case of <=100 rerun collections — the same call site, one defect earlier.
+function loadAllRerunCollections(signal?: AbortSignal): Promise<RerunCollection[]> {
+  return loadAllPages(getRerunCollections, undefined, undefined, signal).then(({ complete, items }) => {
+    if (!complete && !signal?.aborted) {
+      // #644 follow-up F4: a partial result is otherwise indistinguishable from a complete one —
+      // log it so a stalled/incomplete rerun-collections load doesn't silently render as whole.
+      // A superseded/aborted load (retry, or a newer boot supersedes this one — see the abort
+      // below) also returns `complete: false`; that's expected, not a defect, so don't warn on it
+      // (round-3 review F3).
+      console.warn('SchedulesScreen: rerun-collections picker load did not complete; some items may be missing');
     }
-
-    all = [...all, ...nextPage];
-    pageNum += 1;
-  }
-
-  return all;
+    return items;
+  });
 }
 
 type BootState =
@@ -83,10 +75,10 @@ type BootState =
 // getFillerPresetsByKind) hit endpoints that return a plain, unpaged array server-side — no
 // pageNum/pageSize params, no clamp — so they aren't subject to the same silent-truncation defect
 // as rerun collections and don't need the same treatment (ersatztv#634).
-async function loadPickerData(): Promise<SchedulePickerData> {
+async function loadPickerData(signal?: AbortSignal): Promise<SchedulePickerData> {
   const [rerunCollections, playlistGroups, watermarks, graphicsElements, languages, pre, mid, post, tail, fallback] =
     await Promise.all([
-      loadAllRerunCollections(),
+      loadAllRerunCollections(signal),
       getPlaylistGroups(),
       getWatermarks(),
       getGraphicsElements(),
@@ -136,6 +128,13 @@ export function SchedulesScreen() {
   // Last-seen concurrency ETag: set from the items GET, replaced by every successful save's response
   // ETag (a same-tab second save must use the new tag or it would 412 against its own write) (#253).
   const etagRef = useRef<string | null>(null);
+  // Monotonic request id + AbortController for the bootstrap load (spa-conventions §3 / #644
+  // follow-up F2, F3): the Retry button can re-trigger `loadBootstrap` while a previous call
+  // (whose `loadAllRerunCollections` may still be mid-loop) is in flight — abort the stale
+  // controller so it stops issuing further paging requests, and guard on the seq so a stale
+  // resolve can't overwrite a newer one.
+  const bootSeqRef = useRef(0);
+  const bootAbortRef = useRef<AbortController | null>(null);
 
   const setDirtyState = useCallback((value: boolean) => {
     dirtyRef.current = value;
@@ -146,6 +145,7 @@ export function SchedulesScreen() {
     activeRef.current = true;
     return () => {
       activeRef.current = false;
+      bootAbortRef.current?.abort();
     };
   }, []);
 
@@ -153,16 +153,21 @@ export function SchedulesScreen() {
   // Only sets state in promise callbacks (never synchronously in the effect body — see
   // spa-conventions.md §3). The retry button flips to 'loading' itself before calling this.
   const loadBootstrap = useCallback(() => {
-    Promise.all([getSchedules(), loadPickerData()])
+    bootAbortRef.current?.abort();
+    const controller = new AbortController();
+    bootAbortRef.current = controller;
+    const seq = (bootSeqRef.current += 1);
+
+    Promise.all([getSchedules(), loadPickerData(controller.signal)])
       .then(([schedules, pickers]) => {
-        if (!activeRef.current) {
+        if (!activeRef.current || bootSeqRef.current !== seq) {
           return;
         }
         setBoot({ status: 'ready', schedules, pickers });
         setActiveId((current) => current ?? schedules[0]?.id ?? null);
       })
       .catch((error: unknown) => {
-        if (activeRef.current) {
+        if (activeRef.current && bootSeqRef.current === seq) {
           setBoot({ status: 'error', error: messageFromScheduleError(error, 'Unable to load schedules') });
         }
       });